Monday, June 11, 2018

Antibiotics do not sterilize the skin of shoulders undergoing joint replacement

These authors state that propionibacterium is the most common bacteria associated with infection after shoulder arthroplasty.

They conducted a randomized controlled trial in an effort to determine whether adding preoperative intravenous doxycycline to their standard intravenous cefazolin reduced the prevalence of positive propionibacterium cultures of skin and deep tissues at the time of prosthetic joint implantation.

Patients had a standard skin preparation with both alcohol and chlorhexidine. After the infusion of systemic antibiotics, specimens were taken, for aerobic and anaerobic cultures, via (1) an excisional tissue biopsy of the skin edge, (2) a tissue swab of the superficial dermal tissue within the incision, and (3) a tissue swab of the glenohumeral joint. All cultures were maintained for 14 days.

Twenty-one shoulders (38%) had at least 1 positive culture for propionibacterium.The greatest numbers of culture-positive samples were obtained from the skin (30%), followed by dermal tissue (20%) and the glenohumeral joint (5%).

There was no significant difference in culture positivity between the group treated with cefazolin alone (10 [37%] of 27 patients) and the combined doxycycline and cefazolin group (11 [38%] of 29 patients) (p = 0.99).

Propionibacterium culture positivity was significantly more frequent for younger patients, males, and patients with a lower comorbidity index.

Comment: This study demonstrates that systemic antibiotics fail to eliminate the propionibacterium that inhabit the sebaceous glands of normal skin. Likewise, this and prior studies have shown that skin surface preparation fails to eliminate these bacteria. As a result of these two failures, the skin incision for shoulder arthroplasty can transect these sebaceous glands allowing the propionibacterium to inoculate the arthroplasty wound and potentially form a resistant biofilm on the implants.

It is well known that propionibacterium are sensitive to cephalosporins (see this link) so the question is not whether additional antibiotics would help, but rather whether systemic antibiotics penetrate the sebaceous glands sufficiently to kill the bugs there. The answer appears to be "no".
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